Master of Science / Department of Architectural Engineering / Donald J. Phillippi / For this thesis, research was performed on CFRP bonded composite lap-joints with one and two continuous laminas through the lap. Composite wraps used to retrofit existing structures use lap joints to maintain their integrity. The use of composites for retrofitting structures has many advantages over traditional methods, such as steel jacketing, and is becoming more widely accepted in the structural engineering industry. While much literature exists documenting the performance of composite wraps as a whole when applied to concrete columns, less information is available on the behavior of the lap-joint of the wrap. Developing a better understanding of how the lap-joint behaves will help researchers further understand composite column wraps. This research sought to determine what affect continuous middle laminas may have on the stiffness of lap joints and whether or not stress concentrations exist in the lap-joint due to a change in stiffness.

Excellent properties of Carbon Fiber Reinforced Polymer (CFRP) composites are usually obtained in the direction at which carbon fibers are embedded in the polymeric matrix material. The outstanding properties of this material such as high strength to weight ratio, high stiffness and high resistance to corrosion can be tailored to meet specific design applications. Despite their excellent mechanical properties, application of CFRPs has been limited to more lucrative sectors such as aerospace and automotive industries. This is mainly due to the high costs involved in manufacturing of this material. Machining, milling and drilling, is a critical part of finishing stage of manufacturing process. Milling and drilling of CFRP is complicated due to the inhomogeneous nature of the material and extreme abrasiveness of carbon fibers. This is why CFRP parts are usually made near net shape. However, no matter how close they are produced to the final shape, there still is an inevitable need for some post machining to obtain dimensional accuracies and tolerances. Problems such as fiber-matrix debonding, subsurface damage, rapid tool wear, matrix cracking, fiber pull-out, and delamination are usually expected to occur in machining CFRPs. These problems can affect the dimensional accuracy and performance of the CFRP part in its future application. To improve the efficiency of the machining processes, i.e. to reduce the costs and increase the surface quality, researchers began studying machining Fiber Reinforced Polymer (FRP) composites. Studies into FRPs can be divided in three realms; analytical, experimental and numerical. Analytical models are only good for a limited range [0° – 75°] of Fiber Orientations , to be found from now on as “FO” in this thesis. Experimental studies are expensive and time consuming. Also, a wide variety of controlling parameters exist in an experimental machining study; including cutting parameters such as depth of cut, cutting speed, FO, spindle speed, feed rate as well as tool geometry parameters such as rake angle, clearance angle, and tool edge/nose radius. Furthermore, the powdery dust created during machining is known to cause serious health hazards for the operator. Numerical models, on the other hand, offer the unique capability of studying the complex interaction between the tool and workpiece as well as chip formation mechanisms during the cut. Large number of contributing parameters can be included in the numerical model without wasting material. Three main objectives of numerical models are to predict principal cutting force, thrust force and post-machining subsurface damage. Knowing these, one can work on optimization of machining process by tool geometry and path design. Previous numerical studies mainly focus on the orthogonal cutting of FRP composites. Thus, the existing models in the literature are two-dimensional (2D) for the most part. The 2D finite element models assume plain stress or strain condition. Accordingly, the reported results cannot be reliable and extendable to real cutting situations such as drilling and milling, where oblique cutting of the material occurs. Most of the numerical studies to date claim to predict the principle cutting forces fairly acceptable, yet not for the whole range of fiber orientations. Predicted thrust forces, on the other hand, are generally not in good agreement with experimental results at all. Subsurface damage is reported by some experimental studies and again only for a limited FO range. To address the lack of reliable force and subsurface damage prediction model for the whole FO range, this thesis aims to develop a 3D finite element model, in hope of capturing out-of-plane displacements during stress formation in different material phases (Fiber, Matrix and the Interface bonding). ABAQUS software was chosen as the most commonly used finite element simulation tool in the literature. In present work a user-defined material subroutine (VUMAT) is developed to simulate behavior of carbon fibers during the cut. Carbon fibers are assumed to behave transversely isotropic with brittle (perfectly elastic) fracture. Epoxy matrix is simulated with elasto-plastic behavior. Ductile and shear damage models are also incorporated for the matrix. Surface-based cohesive zone technique in ABAQUS is used to simulate the behavior of the zero-thickness bonding layer. The tool is modeled as a rigid body. Mechanical properties were extracted from the literature. The obtained numerical results are compared to the experimental and numerical data in literature. The model is capable of capturing principal forces very well. Cutting force increases with FO from zero to 45° and then decreases up to 135°. The simulated thrust forces are still underestimated mainly due to the fiber elastic recovery effect. Also, the developed 3D model is shown to capture the subsurface damage generally by means of a predefined dimensionless state variable called, Contact Damage (CSDMG). This variable varies between zero to one. It is stored at each time step and can be called out at the end of the analysis. It was shown that depth of fiber-matrix debonding increases with increase in FO. / Graduate

A study to investigate the behavior of glass fiber reinforced polymer (GFRP) anchors was conducted at the Ferguson Structural Engineering Laboratory as part of a project funded by the Texas Department of Transportation, Project number 0-6873. The purpose of this study was to test the effectiveness of GFRP anchors by comparing their performance to that of anchors made from carbon fiber reinforced polymer (CFRP). The findings of this research give insight into the advantages and disadvantages of using alternative materials in the design of FRP anchorage systems and provides a means for developing quality control procedures of GFRP anchors. Quantitative comparisons were made between results from beam tests that used GFRP anchors and the results from those that used CFRP anchors. It was found that specimens with GFRP anchors exhibited similar trends to specimens with CFRP anchors. Similarities were achieved in concrete cracking loads, strength capacities, and in some cases duration of force transfer, suggesting that GFRP anchors are equally as effective as CFRP anchors for strength development. However, material differences played a major role in the explanation of GFRP and CFRP behavior. Notable advantages in material handling was observed with the GFRP anchors since the fibers were found to be easier to bend as well as easier to install into drilled anchor holes. On the other hand, the lower tensile strength of GFRP presented a potential need for larger sized anchors to achieve the equivalent strength of a CFRP anchor. Finally, a pull-out failure mode was observed in GFRP anchors that had not been previously observed in CFRP anchors. It was suggested that the pull-out failure mode was a function of differences in deformation capacity between the two materials. However, little information regarding the cause of performance differences demonstrates the need for quality control tests for GFRP anchors. As a result, recommendations for further studies were made. / text

<div>Research has shown that many adjacent box beam bridges in Indiana experience premature deterioration. Primarily caused by leaking joints between beams, this deterioration leads to corrosion and/or fracturing of prestressing strands, ultimately resulting in flexural deficiency of the bridge. A testing program was designed to simulate this observed deterioration by constructing test specimens and implementing various strengthening techniques using fiber reinforced polymer (FRP) systems. The objective of this testing program is to investigate the effectiveness of FRP strengthening systems to increase or even regain the full capacity of beams that have effectively lost tension reinforcing steel due to corrosion. The FRP-strengthened beam specimens incorporate the use of near-surface-mounted and externally bonded systems. Reinforcing bars in the beams are excluded or cut to simulate deterioration. Furthermore, two different methods of end anchorage for the externally bonded sheets, FRP fan anchorage and U-wrap anchorage, are investigated. Results and conclusions from the testing program are described in order to help advise best practices in implementing the aforementioned strengthening systems. </div>

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Yes / The bond between FRP bars and concrete, the foremost performance for implementation of such reinforcements to corrosion-free concrete structures, is still unsatisfied due to the weak nature of duplex film in the interface. The existing approaches show low efficiency in improving the microstructures and bond between FRP bars and concrete. To address these issues, this paper provided a new approach for improving the bond between FRP bars and concrete by incorporating nanomaterials, as well as explored the modifying mechanisms and established the bond-slip models. For these purposes, the pull-out test, scanning electron microscope observation, as well as energy dispersive spectrometry analysis were performed. The experimental results demonstrated that the presence of nanomaterials increased the ultimate bond strengths between glass/carbon FRP bars and concrete by up to 16.2% and 37.8%, while the corresponding slips decreased by 28.7% and 35.4%, respectively. Such modification effects can be attributed to the optimized intrinsic composition and the reduced pore content of hydration products in the interface, especially in the duplex film, through the nanomaterial enrichment and nano-core effects. The bond-slip relationship between FRP bars and concrete with nanomaterials can be accurately predicted by the mBPE model. / The authors would like to thank the funding offered by the National Science Foundation of China (51978127 and 51908103), and the Fundamental Research Funds for the Central Universities (DUT21RC(3) 039).

Two 7" deep FRP deck panels were manufactured and tested in a controlled service environment. The deck panels were 15' by 5' in plan, and were composed of ten 15' long, 6" by 6" by 3/8" standard pultruded FRP tubes. The tubes were sandwiched between two 3/8" thick standard pultruded FRP plates. The material constituents of the FRP were E-glass fibers in a polyester matrix. When subjected to two strength tests, the first deck panel exhibited a safety factor with respect to legal truck loads of greater than 10. The second deck was subjected to AASHTO design loads, and under a simulated HS-25 axle plus impact the deck exhibited a maximum deflection of L/470. Upon completion of the laboratory testing, the second deck was placed in the field for further study. The maximum strain recorded during field testing was approximately 600 microstrain, which is less than 15% of the ultimate tensile strain of the FRP in its weakest direction. After being subjected to approximately 4 million load cycles (assuming 100,000 5-axle truck crossings per month) over a period of 8 months, the deck exhibited no loss in stiffness. In two post-service strength tests, the second deck exhibited a safety factor with respect to legal truck loads of greater than 8 and greater than 13. / Master of Science

This thesis presents research completed on the experimental performance of two 6 3/4 in thick bridge deck panels fabricated by the Stongwell Corporation of Bristol, Virginia. The panels are made of off-the-shelf, pultruded glass fiber-reinforced polymer elements, bonded and mechanically fastened together. The testing involved laboratory stiffness tests performed on one deck panel which afterwards, was placed in a field test site at the I-81 Troutville Weigh Station facility. The daily truck traffic over the deck panel at this site is approximately 5400 vehicles. The second deck panel was constructed as a prototype to test benefits of steel thru-rod mechanical connectors. Further, a rubber tire loading patch was developed for the laboratory stiffness and strength tests performed on this second specimen to investigate modes of failure. Both decks made use of a hook bolt type connection to steel support beams in order to reduce damage seen in previous methods of connection. / Master of Science

The American Concrete Institute (ACI) has developed guidelines for the design of fiber reinforced polymer (FRP) reinforced concrete structures. Current guidelines require the application of environmental and flexural strength reduction factors, which have minimal experimental validation. Our goal in this research is the development of a Monte Carlo simulation to assess the durability of glass fiber reinforced polymer (GFRP) reinforced concrete designed for flexure. The results of this simulation can be used to determine appropriate flexural strength reduction factors. Prior to conducting the simulation, long-term GFRP tensile strength values needed to be ascertained. Existing FRP tensile strength models are limited to short-term predictions. This study successfully developed a power law based-FRP tensile strength retention model using currently available tensile strength data for GFRP exposed to variable temperatures and relative humidity. GFRP tensile strength retention results are projected at 0, 1, 3, 10, 30, and 60-year intervals. The Monte Carlo simulation technique is then used to assess the influence beam geometry, concrete strength, fractions of balanced reinforcement ratio, reinforcing bar tensile strength, and environmental reduction factors on the flexural capacity of GFRP reinforced concrete beams. Reliability analysis was successfully used to determine an environmental reduction factor of 0.5 for concrete exposed to earth and weather. For simulations with higher GFRP bar tensile strength as well as larger beam geometry and fractions of the balanced reinforcement ratio, larger moment capacities were produced. A strength reduction factor of approximately 0.8 is calculated for all fractions of balanced reinforcement ratio. The inclusion of more long-term moisture data for GFRP is necessary to develop a more cohesive tensile strength retention model. It is also recommended that longer life cycles of the GFRP reinforced concrete beams be simulated. This research was conducted thanks to support from the National Science Foundation Division of Graduate Education's Interdisciplinary Graduate Education Research and Traineeship (Award # DGE-0114342) Note: The opinions expressed herein are the views of the authors and should not be interpreted as the views of the National Science Foundation. / Master of Science